This invention relates generally to photovoltaic or solar cell arrays, and more particularly, the invention relates to energy concentration for use in such arrays.
The use of photovoltaic cells for the direct conversion of solar radiation into electrical energy is well known, see Swanson, U.S. Pat. No. 4,234,352 for example. Briefly, the photovoltaic cell comprises a substrate of semiconductive material having a p-n junction defined therein. In the planar silicon cell the p-n junction is formed near a surface of the substrate which receives impinging radiation. Radiated photons create mobile carriers (holes and electrons) and the substrate which can be directed to an electrical circuit outside of the cell.
In practical applications, photovoltaic cells are arranged in modules with the cells being serially connected to increase output voltage and with a plurality of serially connected cells connected in parallel to increase output current. Efficiency of the arrays can be enhanced by using an energy concentrator with each cell, and the cost of high-efficiency solar cells can be reduced through use of less costly optics.
The parabolic reflector is a known structure for use in concentrating energy. As shown in FIG. 1A, a linear parabolic reflector or trough concentrates energy along a linear axis, and is useful for heating fluids in a pipe, for example, and in low concentration photovoltaic systems. In FIG. 1B, a dish-shaped parabolic reflector concentrates energy at a focal point and is useful for concentrating sound and radio waves. While useful in concentrating solar energy, heretofore the use of the parabolic reflector in a cell array panel requires too much space for practical application.